NETB362

Daemons

Zlatin Stanimirov, F64571

Table of contents:

• Downloads
• Creating half daemons
• Daemonizing in the source code
• Daemonizing in initialization 
• Cron 101
• Tasks

There are code listings to help you get started. You need root privileges to install 2 packages

Downloads:

You may download a small perl script which can be used as a daemon here: https://gist.github.com/IamBc/940820c33b79b9225f55

Perl

• Is the only scripting language installed in all *nix systems
• Favored amongst system administrators 

Run the source code by typing: perl <file name>.pl  in a terminal window.

Daemonize by hand

• Redirect STDIN, STDOUT and STDERR
• Run in background

There are a few things which are easy to do by hand.

You can use the script on the previous slide or make your own.

Daemonize with nohup

What you get:

• The program may continue to run if you have exited the terminal.

What you don't get:

• Tasks aren't ran in bg automatically
• You still need to redirect things

Daemonize in the source code

Your programming language needs to support it. Usually it doesn't by default, but there are a lot of modules. Here are some examples:

• Go https://github.com/sevlyar/go-daemon
• perl http://search.cpan.org/dist/Proc-Daemon/lib/Proc/Daemon.pod
• ruby emons.rubyforge.org/Daemons.html
• C  http://stackoverflow.com/questions/17954432/creating-a-daemon-in-linux

Case study

I suggest to daemonize the script in the beginning of the slides with the module Proc::Daemon, although feel free to do it in any language you like :)

To install the perl library, you need to install the following package with a package manager of your choice:

                                                                libproc-daemon-perl

Daemonize in initialization

We are going to use daemonize.

To install run sudo apt-get install daemon

Daemonize a script by your choice

Cron 101

• Daemon that does periodic jobs
• For more info type man cron in a terminal
• Turn a script to a cron job

Questions ?